I believe the policy is 1 in F and at least 2 in Y on most flts. No pets in BF on the 777. Unless it's been changed, I don't think it's 1 per cabin. As far as the allergies, most airlines would just try to move you to another seat. There are usually an overwhelming number of pet lovers that are not bothered to have a small cat or dog nearby and would be willing to switch to a similar type seat in Y.